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Extratropical Cyclones and Anticyclones

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Extratropical Cyclones and Anticyclones © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION Courtesy of Jeff Schmaltz, the MODIS Rapid Response Team at NASA GSFC/NASA Extratropical Cyclones 10 and Anticyclones CHAPTER OUTLINE INTRODUCTION A TIME AND PLACE OF TRAGEDY A LiFE CYCLE OF GROWTH AND DEATH DAY 1: BIRTH OF AN EXTRATROPICAL CYCLONE ■■ Typical Extratropical Cyclone Paths DaY 2: WiTH THE FI TZ ■■ Portrait of the Cyclone as a Young Adult ■■ Cyclones and Fronts: On the Ground ■■ Cyclones and Fronts: In the Sky ■■ Back with the Fitz: A Fateful Course Correction ■■ Cyclones and Jet Streams 298 9781284027372_CH10_0298.indd 298 8/10/13 5:00 PM © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION Introduction 299 DaY 3: THE MaTURE CYCLONE ■■ Bittersweet Badge of Adulthood: The Occlusion Process ■■ Hurricane West Wind ■■ One of the Worst . ■■ “Nosedive” DaY 4 (AND BEYOND): DEATH ■■ The Cyclone ■■ The Fitzgerald ■■ The Sailors THE EXTRATROPICAL ANTICYCLONE HIGH PRESSURE, HiGH HEAT: THE DEADLY EUROPEAN HEAT WaVE OF 2003 PUTTING IT ALL TOGETHER ■■ Summary ■■ Key Terms ■■ Review Questions ■■ Observation Activities AFTER COMPLETING THIS CHAPTER, YOU SHOULD BE ABLE TO: • Describe the different life-cycle stages in the Norwegian model of the extratropical cyclone, identifying the stages when the cyclone possesses cold, warm, and occluded fronts and life-threatening conditions • Explain the relationship between a surface cyclone and winds at the jet-stream level and how the two interact to intensify the cyclone • Differentiate between extratropical cyclones and anticyclones in terms of their birthplaces, life cycles, relationships to air masses and jet-stream winds, threats to life and property, and their appearance on satellite images INTRODUCTION What do you see in the diagram to the right: a vase or two faces? This classic psychology experiment exploits our amazing ability to recognize visual patterns. Meteorologists look for patterns in weather observations. Instead of pondering “is that a nose, or the narrow part of a vase?” the meteorologist asks, “Is this a line of rain showers? Could that be a wind shift? Should I be focusing on the areas of warm and cold air or the regions in between?” Finding the “face” in the weather is a lot more confusing than in a textbook diagram! Early 20th-century weather forecasting reflected this confusion. Some meteorologists focused on the location and shape of low-pressure areas. Others scrutinized temperature patterns; still others looked at cloud types. No one yet saw the overall “face,” only these individual weather features. In 1918, 20-year-old meteorologist Jacob “Jack” Bjerknes (see photo; pronounced BYURK-nizz) discovered the “face in the clouds” of his native Norway: the extratropical cyclone or low-pressure system. His conceptual model of this type of cyclone emphasized the importance of the fronts that extend like a moustache from the center of midlatitude lows on a weather map. 9781284027372_CH10_0298.indd 299 8/10/13 5:00 PM © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION 300 CHAPTER 10 Extratropical Cyclones and Anticyclones Jack and his father Vilhelm’s “Bergen School” of meteorology fleshed out this face using their intuition and observations of the sky. They realized that the extratropical cyclone, like a face, has a distinctive three-dimensional shape. Furthermore, like a person, the cyclone matures from youth to old age in a recognizable and predictable way. At last, meteorology knew what face to look for! Weather maps and forecasts have never been the same since. In this chapter, we learn how to recognize the face of the extratropical cyclone. To make this face come alive for you, we look at weather data leading up to a tragic day in American history: November 10, 1975. On that day, a cyclone fitting Bjerknes’s description ravaged the midwestern United States and contributed to the wreck of the Great Lakes iron ore freighter Edmund Fitzgerald. Twenty-nine sailors perished on the Fitzgerald without a single “mayday.” More than 35 years later, this tragedy lives on through television documentaries, books, and folk songs. We learn here what the face of a classic cyclone looks like from a variety of angles and why it looks that way. (Courtesy of Geophysical Some faces and people are not so memorable, but the impacts they make are. This is also Institute, University of Bergen.) the case with the cyclone’s counterpart, the anticyclone or high-pressure system. Highs look like bland and boring blobs on the weather map, but they can also harbor potentially tragic weather conditions. This chapter ends with an examination of a heat wave in 2003 that quietly killed 70,000 people in western Europe in the space of just a few days. A TIME AND PLACE OF TRAGEDY1 The year is 1975—the Vietnam War ends, and a gallon of gasoline costs 44 cents in the United States. A small upstart computer software company named Microsoft is founded in Albuquerque, New Mexico. Meanwhile, teenagers are starting to buy platform shoes and boogie to the newest pop music fad, “disco.” On the Great Lakes (FIGURE 10-1) in 1975, large boats deliver iron ore from Minnesota to the steel mills and car factories of Indiana, Michigan, and Ohio. Lake Superior, Earth’s broadest lake, serves as a highway for these boats. The pride of the American ore freighters is the 222 meter (729 foot)-long Edmund Fitzgerald (Fi GURE 10-2). Her respected captain, Ernest McSorley, has weathered 44 years on the lakes. His crew of 29 includes six sailors younger than age 30 years, including 22-year-old Bruce Hudson and 21-year-old Mark Thomas (FIGURE 10-3). In November 1975, “Big Fitz” is completing just its 17th full shipping season on Lake Superior. It’s a young boat by Great Lakes standards. The end of the shipping season comes when the “gales of November” howl across the Lake and winter’s icy cold freezes some of the lake surface solid. One trip too many, during a fierce extratropical cyclone, will sink the Fitzgerald and its crew in 160 meters (530 feet) of churning Lake Superior water on November 10, 1975. A LiFE CYCLE OF GROWTH AND DEATH In the 1920s, Jack Bjerknes helped discover that cyclones such as the one that would sink the Fitzgerald often follow a stepwise evolution of development. The left-hand side of TABLE 10-1 shows how Bjerknes himself depicted the Norwegian Cyclone Model life cycle. The cyclone arises as a frontal wave along a stationary front separating cold, dry cP air from warm, moist mT air. It is called a “wave” because the warm sector region between the cold and warm fronts resembles 1Details of the Edmund Fitzgerald’s last voyage used in this chapter are primarily derived from the following books: The Wreck of the Edmund Fitzgerald by Frederick Stonehouse (Avery Color Studios, Marquette, Michigan, reprinted 1997), Gales of November by Robert J. Hemming (Thunder Bay Press, Holt, Michigan, 1981), and the words of Captain Bernie Cooper in The Night the Fitz Went Down by Hugh E. Bishop (Lake Superior, Port Cities, Inc., 2000). 9781284027372_CH10_0298.indd 300 8/10/13 5:00 PM © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION A Life Cycle of Growth and Death 301 ONTARIO Route of the Edmund Fitzgerald Wreckage site CANADA Thunder Bay Michipicoten Isle Royale Island Lost at sea 7:20 PM MINNESOTA P E R I O R S U 11-10-75 E Caribou A K Island Two Harbors L Stannard Rock Duluth Whitefish Point Superior Whitefish Bay Departure Marquette 2 PM Sault Ste. Marie 11-09-75 WISCONSIN MICHIGAN 90° W 85° W CANADA LAKE SUP ERIO MINNESOTA R MICHIGAN L A K E H 45° N N U 45° N A R G O I MICHIGAN N H WISCONSIN C I M E K A Madison L Detroit LAKE Toledo IOWA ERIE Chicago Gary OHIO ILLINOIS INDIANA 90° W85° W FIGURE 10-1 Map of the Great Lakes region, showing the path of the Edmund Fitzgerald’s final voyage and locations referred to in this chapter. FIGURE 10-2 The ore freighter Edmund Fitzgerald, in a photograph provided by Ruth Hudson, mother of Fitzgerald sailor Bruce Hudson (Figure 10-3). (Courtesy of Ruth Hudson.) 9781284027372_CH10_0298.indd 301 8/10/13 5:00 PM © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION 302 CHAPTER 10 Extratropical Cyclones and Anticyclones a gradually steepening ocean wave. In adolescence, the open wave develops strong cold and warm fronts with obvious wind shifts as the entire system moves to the east or northeast. Precipitation (in green shading) falls in a broad area ahead of the warm front and in a narrow line in the vicinity of the cold front. At full maturity, the occluded cyclone sprouts an occluded front, which Bjerknes conceived of as the result of the cold front outrunning the warm front. Usually, the barometric pressure at the center of the cyclone reaches its minimum during this stage, sometimes plummeting to 960 mb or below in a few intense cyclones—as low as in the eye of a Category 3 hurricane! Because of the strong gradient of pressure near its center, the cyclone’s winds are usually strongest during this stage. The accompanying satellite images in Table 10-1 reveal how the cloudiness associated with the fronts progressively wraps poleward and around the back side of the cyclone. In the final stage, the cut-off cyclone slowly dies a frontless death, as clouds and precipitation around the low’s center dissipate. The life cycle shown in Table 10-1 is an idealized conceptual model. Some real- life cyclones do not follow this life cycle in every detail.
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